In the prior-art chain wheel assembly units of this class, the directional locking mechanism comprises a ratchet wheel connected to the chain wheel to rotate in unison with it and a detent pawl, which elastically engages the teeth of the ratchet wheel and is mounted on a bearing journal of the drive gear.
The drive gear itself is fastened to the shaft in an axially fixed manner. In most embodiments of the prior-art chain wheel assembly units, the drive gear is either pressed directly onto the shaft or is fastened to a bearing bush, which is in turn pressed onto the shaft.
The two profiled disks enclosing the chain wheel between them have a ring-shaped contact shoulder each, on which the link chain engaging the chain wheel and guided over the chain wheel is supported. In addition, these profiled disks are provided with a movable flange each, which adjoins the support shoulder and is used to guide the vertically extending chain sections in the area of the chain wheel.
The circular ring-shaped sections located within the support shoulders have different designs in the two profiled disks. While the ratchet wheel of the directional locking mechanism, which is in contact with a ring wall located in the same plane as the movable flange, is arranged on the outside at the profiled disk facing the drive gear, the opposite profiled disk in the center is provided with an outwardly slightly conically embossed ring section.
The two profiled disks, the chain wheel located between them, and the ratchet wheel are fastened to a common bearing bush, which is seated loosely on a common shaft, and they are adapted to rotate in unison.
These four components form a subassembly unit with the bearing bush which holds them together, while a second subassembly unit is formed by the shaft and the pressed-on drive gear, on which the detent pawl of the directional locking mechanism and the contact spring acting on the detent pawl are mounted and fastened. The spring which holds these two assembly units together on the common shaft comprises a central, perforated ring disk with three or more radial flexible tongues, which are in contact with the movable flange of the profiled disk facing it while the central ring disk is supported at a lock washer seated in a groove of the shaft.
Thus, this prior-art chain wheel assembly unit comprises a total of 10 individual parts, five of which, namely, the two profiled disks, the chain wheel located between them, and the ratchet wheel of the directional locking mechanism, must be mounted and connected with a bearing bush to form a first subassembly unit, while the other four components, namely, the shaft, the drive gear, the detent pawl and the detent pawl spring, must be fitted together into a second subassembly unit before the entire chain wheel assembly unit can be completed by means of the spring and the lock washer. In addition, to achieve a better press fit of the drive gear, the shaft must be provided with a fluting in the section in which the gear is seated.
These prior-art chain wheel assembly units are very expensive to manufacture, partly because they comprise many individual components and partly because they require a considerable assembly work.
A chain wheel assembly unit has also been known (DE Patent No. 25 100), in which the chain wheel comprises two conical, cast disks which form a hollow space of a wedge-shaped cross section between them, in which the weight chain is guided in an entrained manner. The directional locking mechanism, via which the drive gear seated firmly on its shaft is in drive connection with the chain wheel, may consist of a ring of ratchets, which is arranged on the front surface of the chain wheel and is held engaged with the spokes of the drive gear by an axially acting compression spring.
According to another embodiment, the chain wheel has a ring of ratchets on its front side facing away from the drive gear. This ratchet ring is engaged by two fingers of a leaf spring in the manner of detent pawls, which are fastened on the shaft, rotating in unison with it, by means of a pin connection.
This design is also complicated especially in terms of assembly.